1. Field of the Invention
The present invention relates generally to an evaporative type cooling system for an internal combustion engine wherein liquid coolant is permitted to boil and the vapor used as a vehicle for removing heat therefrom, and more specifically to such a system which is able to prevent localized concentration of anit-freeze in the coolant jacket due to the distillation-like process which characterizes the cooling of evaporation type systems.
2. Description of the Prior Art
In currently used "water cooled" internal combustion engines such as shown in FIG. 1 of the drawings, the engine coolant (liquid) is forcefully circulated by a water pump, through a cooling circuit including the engine coolant jacket and an air cooled radiator. This type of system encounters the drawback that a large volume of water is required to be circulated between the radiator and the coolant jacket in order to remove the required amount of heat. Further, due to the large mass of water inherently required, the warm-up characteristics of the engine are undesirably sluggish. For example, if the temperature difference between the inlet and discharge ports of the coolant jacket is 4 degrees, the amount of heat which 1 Kg of water may effectively remove from the engine under such conditions is 4 Kcal. Accordingly, in the case of an engine having an 1800 cc displacement (by way of example) is operated full throttle, the cooling system is required to remove approximately 4000 Kcal/h. In order to achieve this, a flow rate of 167 liter/min (viz., 4000-60.times.1/4) must be produced by the water pump. This of course undesirably consumes a number of otherwise useful horsepower.
Further, the large amount of coolant utilized in this type of system renders the possibility of quickly changing the temperature of the coolant in a manner that instant coolant temperature can be matched with the instant set of engine operational conditions such as load and engine speed, completely out of the question.
FIG. 2 shows an arrangement disclosed in Japanese Patent Application Second Provisional Publication No. 57-57608. This arrangement has attempted to vaporize a liquid coolant and use the gaseous form thereof as a vehicle for removing heat from the engine. In this system the radiator 1 and the coolant jacket 2 are in constant and free communication via conduits 3, 4 whereby the coolant which condenses in the radiator 1 is returned to the coolant jacket 2 little by little under the influence of gravity.
This arrangement while eliminating the power consuming coolant circulation pump which plagues the above mentioned arragement, has suffered from the drawbacks that the radiator, depending on its position with respect to the engine proper, tends to be at least partially filled with liquid coolant. This greatly reduces the surface area via which the gaseous coolant (for example steam) can effectively release its latent heat of vaporization and accordingly condense, and thus has lacked any notable improvement in cooling efficiency.
Further, with this system in order to maintain the pressure within the coolant jacket and radiator at atmospheric level, a gas permeable water shedding filter 5 is arranged as shown, to permit the entry of air into and out of the system. However, this filter permits gaseous coolant to readily escape from the system, inducing the need for frequent topping up of the coolant level.
A further problem with this arrangement has come in that some of the air, which is sucked into the cooling system as the engine cools, tends to dissolve in the water, whereby upon start up of the engine, the dissolved air tends to come out of solution and form small bubbles in the radiator which adhere to the walls thereof and form an insulating layer. The undissolved air also tends to collect in the upper section of the radiator and inhibit the convection-like circulation of the vapor from the cylinder block to the radiator. This of course further deteriorates the performance of the device.
Moreover, with the above disclosed arrangement the possibility of varying the coolant temperature with load is prevented by the maintainance of the internal pressure of the system constantly at atmospheric level.
European Patent Application Provisional Publication No. 0 059 423 published on Sept. 8, 1982 discloses another arrangement wherein, liquid coolant in the coolant jacket of the engine, is not forcefully circulated therein and permitted to absorb heat to the point of boilings. The gaseous coolant thus generated is adiabatically compressed in a compressor so as to raise the temperature and pressure thereof and thereafter introduced into a heat exchanger (radiator). After condensing, the coolant is temporarily stored in a reservoir and recycled back into the coolant jacket via a flow control valve.
This arrangement has suffered from the drawback that when the engine is stopped and cools down the coolant vapor condenses and induces sub-atmospheric conditions which tend to induce air to leak into the system. This air tends to be forced by the compressor along with the gaseous coolant into the radiator. Due to the difference in specific gravity, the air tends to rise in the hot environment while the coolant which has condensed moves downwardly. The air, due to this inherent tendency to rise, forms pockets of air which cause a kind of "embolism" in the radiator and which badly impair the heat exchange ability thereof. With this arrangement the provision of the compressor renders the control of the pressure prevailing in the cooling circuit for the purpose of varying the coolant boiling point with load and/or engine speed difficult.
U.S. Pat. No. 4,367,699 issued on Jan. 11, 1983 in the name of Evans (see FIG. 3 of the drawings) discloses an engine system wherein the coolant is boiled and the vapor used to remove heat from the engine. This arrangement features a separation tank 6 wherein gaseous and liquid coolant are initially separated. The liquid coolant is fed back to the cylinder block 7 under the influence of gravity while the relatively dry gaseous coolant (steam for example) is condensed in a fan cooled radiator 8.
The temperature of the radiator is controlled by selective energizations of the fan 9 which maintains a rate of condensation therein sufficient to provide a liquid seal at the bottom of the device. Condensate discharged from the radiator via the above mentioned liquid seal is collected in a small reservoir-like arrangement 10 and pumped back up to the separation tank via a small constantly energized pump 11.
This arrangement, while providing an arrangement via which air can be initially purged to some degree from the system tends to, due to the nature of the arrangement which permits said initial non-condensible matter to be forced out of the system, suffers from rapid loss of coolant when operated at relatively high altitudes. Further, once the engine cools air is relatively freely admitted back into the system. The provision of the bulky separation tank 6 also renders engine layout difficult.
Further, the rate of condensation in the consensor is controlled by a temperature sensor disposed on or in the condensor per se in a manner which holds the pressure and temperature within the system essentially constant. Accordingly, temperature variation with load is rendered impossible.
Japanese Patent Application First Provisional Publication No. 56-32026 (see FIG. 4 of the drawings) discloses an arrangement wherein the structure defining the cylinder head and cylinder liners are covered in a porous layer of ceramic material 12 and wherein coolant is sprayed into the cylinder block from shower-like arrangements 13 located above the cylinder heads 14. The interior of the coolant jacket defined within the engine proper is essentially filled with gaseous coolant during engine operation at which time liquid coolant sprayed onto the ceramic layers 12.
However, this arrangement has proven totally unsatisfactory in that upon boiling of the liquid coolant absorbed into the ceramic layers, the vapor thus produced and which escapes into the coolant jacket, inhibits the penetration of fresh liquid coolant and induces the situation wherein rapid overheat and thermal damage of the ceramic layers 12 and/or engine soon results. Further, this arrangement is of the closed circuit type and is plagued with air contamination and blockages in the radiator similar to the compressor equipped arrangement discussed above.
FIG. 7 shows an arrangement which is disclosed in U.S. Pat. No. 4,549,505 filed on Oct. 29, 1985 in the name of Hirano. The disclosure of this application is hereby incorporated by reference thereto.
For convenience the same numerals as used in the above mentioned Patent are also used in FIG. 7.
This arrangement while solving the problems encountered with the above described prior art has itself encountered the drawback that in the event that a solution water and ethylene glycol (for example) anti-freeze is used, as the latter mentioned substance is non-azeotropic, the vapor produced in the coolant jacket 120 contains a greatly reduced amount of anti-freeze as compared with the liquid coolant therein and accordingly, as time passes a notable concentration of anti-freeze tends to build-up in the coolant jacket 120 leaving the coolant which is contained in the remainder of the system (paticulary the radiator 126 and collection vessel 128 at the bottom thereof) diluted to the point of being apt to freeze in cold environments. Viz., as time goes by, a kind of "distillation" process occurs which dilutes the concentration of coolant in the radiator and associated conduiting which are the most susceptible elements of the engine to the cold. Even when the engine is stopped and the interior of the cooling circuit is filled with coolant from the reservoir 146 still the distribution tends to persist.
FIG. 8 shows an arrangement which although has bascially suffered from the various drawbacks set forth hereinbefore, has attempted to unify the concentration of anti-freeze in the engine coolant by providing a conduit 20 which interlinks the bottom of the radiator or condenser 22 and a section of the coolant jacket 24 whereat the concentration of anti-freeze is proportedly apt to be the highest. With this arrangement it is asserted that the concentration of coolant in the engine radiator or condensor 22 can be maintained essentially equal to the that in the coolant jacket 24.
However, as will be noted with the provision of this "blending" conduit 20 the tendancy for the level of coolant in the coolant jacket 24 and the condensor 22 is apt to become equal. In order to prevent this it would appear that the coolant return pump 26 must have a relatively large capacity and constantly energized so as to ensure that an adequate amount of coolant is constantly retained in the coolant jacket 24 despite the "drain" which is provided by the blending conduit 20.
The application of this concept to the cooling system shown in FIG. 7 of course is impractical as it tends to destroy the control of the liquid coolant level in the radiator 126 and thus the ability of the system to control the heat exchange capacity of the radiator for the purposes of coolant temperature control.